Project 6: Oxidative Remediation of Recalcitrant Contaminants with Persulfate. Persulfate (S20s^) is a relatively inexpensive reagent that can be used to oxidize many of the most recalcitrant contaminants present at hazardous waste sites. Although it is becoming more popular for hazardous waste site remediation, the chemical reactions through which persulfate oxidizes contaminants are not well understood. The overall goal of our research is to develop and test new approaches for oxidizing contaminants that are difficult to treat with existing technologies (e.g., PCBs, 1,4-dioxane and PFOA) and apply it to make treatment systems more robust and efficient. Through the use of kinetic models and detailed research on reaction mechanisms, we will develop the means of predicting contaminant transformation rates and optimizing system performance. This mechanistic understanding of persulfate chemistry will require that we build increasing complexity into our model in stages. Initially, we will calibrate our kinetic model for the homogeneous reactions through which persulfate is converted into oxidants using experiments with various compounds that react predominantly with sulfate radical or hydroxyl radical. After calibrating the model over the range of conditions likely to be encountered during remediation, we will investigate the role of heterogeneous reactions of iron-containing solids on the initiation of radical production. By applying findings from experiments in heterogeneous systems with state-of-the-art surface characterization techniques we will synthesize new types of heterogeneous catalysts for ex situ treatment of contaminated groundwater. We also will use results from the heterogeneous experiments to improve the predictive ability ofthe model and identify optimal conditions for remediation. After defining the conditions that are best suited for contaminant remediation, we will assess the potential formation of toxic intermediate products during the remediation process using high content screening assays and mass spectrometry. Our research will lead to a mechanistic understanding of persulfate chemistry that should, in turn, lead to a level of understanding that will allow engineers to avoid excessive use of reagents and the formation of toxic intermediates when persulfate is used for remediation.